Loudspeaker baffle assembly



g- 1960 N. FRIEDMAN 2,949,163

LOUDSPEAKER BAFFLE ASSEMBLY Filed May 6, 1957 INVENTOR. NORMAN FRIEDMAN BY M Fax L ATTORNEYS United States Patent LOUDSPEAKER BAFFLE ASSEMBLY Norman Friedman, St. Louis, Mo., assignor to Soundolier, Inc., St. Louis, Mo., a corporation of Missouri Filed May 6, 1957, Ser. No. 657,339

2 Claims. (Cl. 181-31) This invention relates to improvements in loud-speaker bafile assemblies especially adapted for commercial and industrial sound systems.

The principal object of the invention is to improve the performance characteristics of loudspeakers for commercial low-powered sound systems, and with that object in View, to provide an improved, relatively small, lowcost bass reflex type baflle of metallic construction. Among the objects achieved and the advantages of the bafiie assembly of the present invention is a frequency response of extended range in both the high and low registers; sound projection in a very wide angle polar pattern, and a more uniform and effective distribution of the sound throughout all parts of the listening area; improved efliciency as compared to existing types of commercial bafiles because of effective utilization of radiation from the rear of the speaker diaphragm, and the substantial elimination of rattle.

The foregoing objects and advantages are realized in an improved baflle structure which includes inner and outer metal shells of annular form which coact to provide a bass reflex mounting enclosure for the speaker, and to form an exponential or other acoustical born for redirecting rear sound radiation to the front, the throat of the horn serving as a bass reflex port for inverting the phase of the radiation produced at the rear side of the speaker diaphragm. The front and rear radiation combine and are projected in a wide angle from the front of the unit with augmented bass response.

Another object is achieved in the provision of an improved baflle assembly of the character described, constructed in an improved manner, to facilitate access to the speaker mounted therein.

The foregoing and other objects and advantages will appear in the following description of a preferred embodiment of the invention, reference being made to the accompanying drawing, in which- Fig. l is a perspective view of the baffle of the present invention;

Fig. 2 is a transverse sectional view of the bathe assembly on a relatively larger scale, the section being taken at line 22 of Fig. 1;

Fig. 3 is a top plan view of the assembly;

Fig. 4 is a plan view of the inner housing top plate member as viewed from the inner side thereof;

Fig. 5 is a side view partly in section taken at line 5-5 of Fig. 4;

Fig. 6 is a rear plan view of the outer enclosure member;-and

Fig. 7 is a side elevational view partly in section of an inner housing member.

Described generally, my improved batfle assembly comprises an inner housing structure in which the loudspeaker is mounted, and an outer enclosure member surrounding the rear wall and sides of the inner housing. Radiation from the front of the speaker diaphragm is projected forwardly through the reticulated front Wall of the inner housing. Radiation from the rear surface of the dia- Patented Aug. 16, 1960 phragm is transmitted through an opening in the rear of the inner housing to a relatively narrow annular space between rear wall portions of the inner housing and outer enclosure member. The rearward radiation is conducted radially through the said restricted space, constituting a bass reflex port and throat portion of an acoustical horn, defined by and between the side wall portions of the inner housing and outer enclosure. The rear radiations thusly redirected through said horn emanate from the front of the assembly. In accordance with established acoustical principles the restricted port effects a phase inversion of the rear low frequency radiation so that it issues from the horn in proper phase relation to combine with and augment the front radiation. Rear radiations which are wasted in other commercial baffles are employed to great advantage with my improved device to improve efficiency, to reenforce and project the low tones and to widen the polar pattern of the speaker.

Continuing now with a description in greater detail of my improved baflie, and with reference to the drawings, the inner housing assembly 11 (Fig. 7) comprises a hollow shell fabricated of sheet metal and coated on the inside with sound deadening material 33. It includes a generally pan-shaped main part having a sloping side Wall 12 and front rim or flange portion 13 that defines a circular opening 14 in the front of the housing. Opening 14 is preferably covered with a screen 15 to afford protection to the diaphragm or" the speaker 16 located to the immediate rear thereof. Speaker 16 has its annular frame part rigidly secured to the front housing rim 13 by the screws 17 which also serve as attachment means for screen 15, the diaphragm or cone of the speaker and its gasket (not shown) providing an air-tight partition at the front of the inner housing 11.

The heretofore described main part of the housing 11 is detachably connected to an annular rear plate 18 (Fig. 4) having a forwardly projecting flange 19 which fits snugly within the rear rim portion of the side wall 12 which is reenforced by a return flange indicated at 20. Means for securing the housing parts 11 and 18 together while permitting them to be easily and quickly detached from each other are provided in the spring latching assemblies 21. These consist of keeper studs 22 mounted on the free ends of leaf springs 23 whose opposite ends are secured to the inner surface of the rim 19. The keeper studs 22 are held by the springs 23 to project outwardly through registering openings in the mating rim portions of parts 11 and 18. By depressing the studs 22 with the fingers the main housing part may be detached and re moved from the rear plate 18 so as to afford access to the speaker. The rear plate 18 is provided with a circular central opening 24 of substantial proportions to provide an opening for sound at the port and throat of the acoustical horn hereinafter described.

The inner housing is positioned concentrically within the pan-shaped outer enclosure member 25. Annular plate 18 of the inner housing is secured in spaced relation to the rear wall 26 of the enclosure 25 by screws 27 that extend through spacer grommets 28 formed of pliable rubher, or other suitable vibration absorbing or dampening material. The grommets 28 isolate the speaker and housing assembly from the enclosure member 25, and aid in preventing distortion and rattles. The heads of screws 27 are recessed in an annular channel 29 in rear wall 26, so that the member may be easily mounted against a flat surface. Key-hole shaped openings 30 in the rear wall 26 accommodate mounting screws for securing the entire assembly to a ceiling or other support.

The sloping side wall 31 of the enclosure 25 projects forwardly in diverging relation to side wall 12 of housing 11, the said walls being suitably shaped to form opposite sides of an annular acoustical horn that provides a low loss path for the highly efiicient transmission of radiation from the rear of the speaker diaphragm to the front of the baffle assembly.

It will be understood that the cros -section of the horn throat between wall portions 18 and 26 increases in effective area from a minimum at the margin of opening 24 to maximum at the outer edge of side wall 31 of enclosure 25.

Consideration should be given to the size of the throat or port area of the bafiie in order to obtain optimum performance of the speaker and baffle combination. As has previously been mentioned, the throat or port is restricted passage designated P between wall portions 18 and 26. The area of this port is determined by the di-- ameter of the opening 24 and the effective length of the rubber spacer grommets 28.

It is known that the throat of an acoustical horn ex hibits a reactance and resistance to the transmission of sound in the region of the cut-off frequency of the horn. In my improved baffle the throat P serves as a port for the described bass reflex housing. This bass reflex construction results in an appreciable strengthening or boost of the bass tones. An equally important advantage of the described construction is the improved polar pattern and overall efficiency of the unit attained by the utilization of the rear radiation of the speaker by the described horn.

As a practical example, an improved bafile embodying my invention, wherein the volume of the inner housing 11 is approximately 300 cubic inches and the diameter of the rear opening 24 is approximately six and one-quarter inches, the distance between rear plates 26 and 18 is desirably fixed at one-quarter of an inch. Due to the insensitiveness of the average human ear an appreciable variation in that dimension will not noticeably detract from the performance of the unit.

It will be understood that certain changes may be made in the baffie herein illustrated and described without departing from the spirit and full intendment of my invention which is defined by the appended claims.

I claim as my invention:

1. In a loud speaker baffle assembly, an inner housing formed of sheet metal and having a front opening, an annular side wall of gradually increasing diameter from front to rear, and a that detachable rear Wall having a '4 central circular opening of smaller area than said front wall opening, said rear and side walls having snugly interfitting rim portions, releasable latching means for securing said rim portions together in assembly, a perforated cover extending across the front opening of said housing, and means for mounting a loud speaker in said housing with the diaphragm thereof extending across and contiguous to said perforated cover; a pan-shaped sheetmetal outer enclosure having an annular side wall of gradually decreasing diameter from front to rear arranged concentrically with respect to said inner housing, and a flat rear wall, studs projecting forwardly from the rear wall of said outer enclosure, the detachable rear wall of said inner housing being mounted on said studs in closely spaced parallel relation to the rear Wall of said outer enclosure, said inner housing having sound-absorbing material on the inner surfaces thereof.

2. A loud speaker bafile assembly as described in claim 1, including relatively flat washers of resilient vibrationabsorbing material on said studs, said washers being compressed between the rear walls of said outer enclosure and inner housing members.

References Cited in the file of this patent UNITED STATES PATENTS 407,611 Rapp July 23, 1889 1,255,910 Morey Feb. 12, 1918 1,834,741 Rigali Dec. 1, 1931 1,843,524 Stenger Feb. 2, 1932 1,943,499 Williams Jan. 16, 1934 2,108,846 Brown Feb. 22, 1938 2,194,070 Giannini Mar. 19, 1940 2,642,948 Olson et a1 June 23, 1953 2,731,101 Klipsch Jan. 17, 1956 FOREIGN PATENTS 643,336 France May 15, 1928 523,482 Great Britain July 16, 1940 OTHER REFERENCES Publication: Hi Fi Loudspeakers and Enclosure by A. B. Cohen. Copyright 1956 by John F. Rider Publisher Inc., New York 13, New York; pages 169 and 177. 

